There has been increasing evidence that natural killer (NK) and killer (K) cell systems can play an important role in the first line of host defense mechanisms against neoplastic growth and metastasis as well as against viral, bacterial, and parasitic infections. Germfree, colostrum-deprived, immunologically "virgin" piglets have absolutely no NK activity but have well-developed K cells mediating antibody-dependent cellular cytotoxicity (ADCC). Therefore, the gnotobiotic miniature swine model presents a unique opportunity for us to investigate the following four specific aims: (1)\further definition of the cellular nature of porcine NK and K cells; (2)\ontogenic development and differentiation of NK and K cells and their cell lineages; (3)\nature of recognition receptors and/or function-associated surface structures of NK cells; and (4)\regulation of NK cell activity in vitro and in vivo. Combinations of a short-term (2.5 to 4 hrs) 51Cr-release assay method for cytolytic effector activity of NK and K cells, a single cell in agarose assay method for target cell binding and cytolytic activity for a single or multiple targets, Percoll gradient fractionation of large granular lymphocytes, "panning" and indirect rosette separation methods for NK and K cell separations and monospecific monoclonal antibodies produced by hybridoma technology, etc., will be used to characterize NK and K cells morphologically, immunologically, and functionally and to determine their cell lineages as well as to define the ontogeny, differentiation and activation, and/or regulatory mechanisms of these important host defense systems. This may eventually lead to manipulation or regulation of natural immunity against neoplastic diseases as well as microbial and parasitic diseases. (LB)